Countercurrent lube extraction with dual solvent system

ABSTRACT

1. A COUNTERCURRENT EXTRACTION PROCESS FOR THE UPGRADING OF A HYDROCARBON OIL COMPRISING CONTACTING SAID OIL WITH A SOLVENT COMPRISING N-METHYL-2-PYRROLIDONE AND WATER, IN AN EXTRACTION ZONE, THEREBY FORMING A SOLVENTOIL MIXTURE, SAID WATER AND SAID N-METHYL-2-PYRROLIDONE INTRODUCED SEPARATELY INTO SAID EXTRACTION ZONE AND WHEREIN SAID WATER IS INTRODUCED AT A POINT BELOW THE POINT OF INTRODUCTION OF SAID N-METHYL-2-PYRROLIDONE, SO AS TO PREVENT SUBSTANTIAL MIXING OF SAID WATER AND SAID AS TO PREVENT SUBSTANTIAL MIXNG OF SAID WATER AND SAID DONE CONTACTING SAID OIL.

Oct. 22,1974 0]. M. M DONALD ET L 3,843,515

COUNTERCURRENT LUBE EXTRACTION WITH DUAL SOLVENT SYSTEH Filed larch 15. 1972 COMPARISON OF WATER INJECFION AND PREMIXING FOR NMP EXTRACTION OF ARAMCO SOON YIELD, LV%

WATER INJECTED WATER PREMIXED TREAT, v%

WATER ADDED, LV% 0N FEED United States Patent O US. Cl. 208326 I 8 Claims ABSTRACT OF DISCLOSURE An improved process for the solvent extraction of petroleum oil fractions is described. Specifically, a solvent comprising N-methyl Z-pyrrolidone' (NMP) and water is contacted with a lube oil feed in order to selectively extract aromatic-type constituents therefrom. The process involves a countercurrent extraction operation and comprises introducing the NMP and water separately into the extraction zone in such a manner that there is no appreciable mixing of the water and NMP with each other prior to the latter, i.e., NMP, contacting the oil. In a preferred embodiment, the water is introduced into the extraction zone at a point below the point of introduction of the NMP and either above or below the point of introduction of the oil feed. Results obtained with'this solvent are compared with phenol and phenolwater solvent systems.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to an improved process for the solvent extraction of an aromatics-containing petroleum oil fraction. More specifically, the process relates to the use of a solvent comprising N-methyl-Z-pyrrolidone and Water to remove at least a portion of the aromatic-type constituents from the lube oil stock. Still more specifically, the process of the invention involves contacting the solvent with the lube oil stock in a countercurrent extraction operation. 1

Description of the prior art It is well known in the art that solvent extraction may bev utilized to separate aromatics from lube oil stocks containing aromatics and saturates in order to improve oxidation properties, color, and viscosity index (V.I. of the oil. In a typical liquid extraction process the degree of aromatics separation from a feed stock depends on several factors in addition to the characteristics of the solvent itself, such as the critical solution temperature of the mixture of components and the number of theoretical or actual stages (plates). The critical solution temperature is defined in Chemical Engineers Handbook, McGraw-Hill Fourth Edition, pages 14-44, l963,'as that temperature above which two relatively immiscible liquids become totally miscible with each other. The miscibility of the extract and raflinate phases is directly related to the critical solution temperature. For most systems, the mutual solubility of the two partially soluble phases increases as the criticalsolution temperature is approached. Above the critical solution temperature the two phases become completely miscible and there is no separation. In general, however, when operating at temperatures below the critical solution temperature and within the region of partial miscibility, if the temperature is increased, the amounts of oil dissolved in the extract phase and of the solvent dissolved in the rafiinate phase are also increased. The importance of temperature is further shown by the fact that the solvent power always increases with an increase in temperature until complete miscibility is reached,

3,843,515 Patented Oct. 22, 1974- region is approached. It is significantly noted that, by raising the critical solution temperature of a particular solvent with a lube oil distillate by the addition of water, it becomes possible to increase the raffinate yield at a given extraction temperature because of the increased solvent selectivity and to improve the settling of the two phases at a higher extraction temperature because of the increased interfacial tension.

Another factor upon which aromatics separation from lube oil stocks is dependent, is the treat or solvent/oil ratio. The minimum quantity of solvent which can be used forextraction depends on the solubility of the solvent in the oil, and the maximum quantity depends on the solubility of the oil in the solvent, as otherwise the separation into two phases would be impossible. It is noted that the solvent/oil ratio is interrelated with the extraction temperature.

Typical of prior art extraction processes are those utilizing phenol and/or phenol-water solvent systems. One such process is disclosed in US. 2,329,606. Specifically, the process comprises introducing a feed stock into an extraction column and contacting the feed therein with phenol. The phenol is introduced into the top of the column and is contacted therein countercurrently with the upward rising feed stock. Simultaneously, phenolic water is introduced near the bottom of the column. The overall object of the process is to improve the efiiciency of a phenol-water solvent extraction system. This is accomplished by providing internal reflux near the bottom of the column by increasing the selectivity of the solvent at that point.

Other solvents that have been used in prior art processes include N-methyl-2-pyrrolidone alone or in comhination with water. Typical of processes using the latter solvents is that disclosed in US. 2,933,448 which 7 teaches the use of gamma-butyrolactam/water solvent systems and specifies two preferred embodiments of the lactam and water solvent system prior to contacting the hydrocarbon feed stock while the second embodiment involves adding the water to the lactam-hydrocarbon mixture.

The 'prior art processes as described supra have, in general, suffered from several economic disadvantages such as the need for high solvent treats and overall low product yields.

SUMMARY OF THE INVENTION carbon feed stock. In one embodiment of the invention,

but the selectivity decreases rapidly as the miscibility substantial mixing of the water and NMP is prevented by introducing the water into the extraction zone at a point below that of the NMP and either above or below the introduction point of the feed stock. Extract and rafiinate phases are formed and the solvents are recovered from the extract and railinate phases and an improved hydrocarbon oil from the rafiinate phase. By operating in this manner, it has been found that substantial improvements in extraction efiiciency are obtained relative to premixing the water and N-methyl-Z-pyrrolidone.

By preventing substantial mixing of the NMP and water is meant that less than about 0.5 LV percent water (based on total NMP introduced into the extraction zone), preferably less than about 0.1 LV percent H O mixes with the NMP prior to the latter contacting the oil. It is noted ployed, such as distillation, to recover the solvent from the extract and raffinate phases. The solvent may be recycled to the extraction zone, if desired. The most preferred solvent system comprises Nmethyl-'2-pyrrolidone in combination with from about 0.5 to about 30% by weight of water, based on total solvent.

The process disclosed herein is designed to remove the more polar compounds from a feed consisting of a mixture of hydrocarbons. Specifically, the process is designed to separate the more aromatic type constituents from a feed containing a mixture of said constituents with nonaromatic, or parafiinic and naphthenic hydrocarbons. More particularly, such feeds will consist of petroleum distillate fractions or lube residua (bright stocks). In general, the distillate fractions will have a boiling range within the broad range of about 400 F. to about 1200" F. The preferred distillate fractions are the lubricating oil fractions boiling within the range of 500 F. and 1100 F.,

containing between 5% and 70% polar aromatic com- A pounds including benzenes, naphthalenes, anthracenes and phcnanthrenes, and with aromatic compounds which range from C to C The lube residua generally boil above 800 F. These fractions and lube residua may come from any source, such as the parafiinic crudes obtained from Aramco, Kuwait, the Panhandle, North Louisiana, Western Canada and the like.

In order'to produce the required contacting, a typical prior art solvent extraction process may be utilized. In

such a system the feed and solvent are contacted in an extraction zone, which may consist of any suitable means to obtain thorough mixing. As indicated previously, countercurrent extraction is preferred. In one embodiment the water is injected continuously near the bottom of the countercurrent extractor coming into countercurrent contact with the NMP; the latter being introduced near the top of the extractor, thereby forming an extract phase and a rafiinate phase. As indicated supra, the water may be introduced into the extractor either above or below the point of introduction of the feed stock. After settling, the two phases are separated and the solvents recovered utilizing any conventional separation process, such as distillation. The solvent may be recovered from the two phases and recycled.

The extraction process is carried out at a temperature such that the feed and the solvent both remain substantially in the liquid phase. In addition, the conditions are such that feed and solvent-water mixture are partially miscible.

It is noted that the extraction temperature islimited by the boiling points of the constituents, and further limited by the critical solution temperatures of the feed and the solvent-water mixture. More particularly, it has been found that certain temperatures within the range thus provided are economically more attractive than others. Specifically, preferred extraction temperature ranges for the various solvent-water mixtures to be employed'in con; junction with this invention are from about 100 F. to about 250 F. It is noted that the temperature ranges em ployed are different for the different solvent-water mixtures. For the following solvent-water mixtures, the temperature ranges that may be employed are as follows:

western Canada paraffin distillates.

The amount of solvent to be employed in conjunction with this invention may vary over a wide range. It is limited, at any given extraction temperature, by the and by the'solubility of the oil in the solvent system on the other and, in addition, by economic considerations. More particularly, it is preferred that the amount of total solvent utilized, i.e., NMP plus water, as shown by the treat or solvent-oil ratio, be between 50% and 1000%.

In conjunction with the present invention, it is noted that, except at very high pressures, the influence of pressure on the liquid-liquid equilibrium is small. But this invention does assume the use of a sufficiently high operating pressure to maintain a substantially condensed system, that is, above'the vapor pressure of the solutions.

In summary, utilization of NMP and water in a countercurrent extraction process wherein the NMP and Water are 'separately'int-roduced into the extractor in the manner hereinabove described, has been found to yield large economic advantages vis-a-vis prior art processes wherein the N MP and water are premixed.

DESCRIPTION OF THE DRAWING The figure compares the extraction efficiency of premixing the water and- NMP vis-a-vis separate water injection, as measured by treat and product yield.

' DESCRIPTION OF THE PREFERRED EMBODIMENT This. invention will be more apparent from the preferred embodiment and working examples as set forth below. In 'a preferred form, NMP will be employed as the selective solvent in combination with between 0.5 wt. percent and 20 Wt. percent water, based on total solvent, so as to raise the critical solution temperatures from between 50 F. and 550 F.

Within the extraction unit, the temperatures to be employed forthe solvent-water mixtures in question are from F. to 250 F. At these conditions the actual number of gallons/hour of the solvent-water mixture and feed streams will'depend upon the scaleof the operation (i.e., commercial scale or pilot scale) and the particular size of the unit utilized but the'treat,'or solvent/oil ratio'employed, will be between 50% and 1000%, and from 1 to 20 stages may be utilized.

The feed stream consists of either lubricating oil fractions boiling within the range of 500 F. to 1100 F., containing between 5% and 70% aromatics, the aromatics ranging froin C to C 0r lube residua generally boiling about 900 F. The two immiscible phases which are formed may be separated and the solvent in each phase recovered by any conventional means, such as distillation.

Thepreferred embodiment is further illustrated by the following examples:

Example 1 V, This example illustrates the method used to deter-mine the selectivity and solvent power of the NMP-Water mixtures herein disclosed. Thirty m1. of waxy IO-grade Western Canadian-distillates of. diifering saturate/aromatic content were mixed with 30 ml. of the solvent in combination with dilfering amounts of water in a batch extractor at atmospheric pressure at a temperature about 100 to F. below the critical solution temperature of the particular solvent-water ratio and the distillate. After the rnitxures settled, the rafiinate and extract phases were separated and the composition of each determined. The refractive indices of the oil in each phase were determined; The refractive indices of the oil in each phase were determined as well as the dewaxed (pour point, 0 F.) viscosity index of the rafiinate oil. A tertiary diagram for the solvent-oil system was thus constructed from these data according to the method of Hunter and Hash, Ind. & Eng. Chem., 27, 836 (1935,). The data are tabulated in Table II.

Baflinate phase Extract phase Dewaxed viscosity Solvent Refractive Solvent Reflective index of index index of oil (wt. oil at 140 F. of oil percent) at 140 F. percent) TABLE II p (a) Results utilizing N-methy1-2-pyrro1idone containing 5% water by weight at an extraction temperature oi 140 F.

' Raflinate phase Extract phase Dewaxed viscosity Solvent Refractive Solvent Refractive index of index wt. index of'oil (wt. oil at 140 F. of oil percent) at 140 F. percent) (b) Results utilizing aqueous N-inethyl-Z-pyrrolidone containing by weight water at anextraction temperature of 140 F.

By use of correlations,between"countercurrent plant extraction operations and the ternary phase diagram for the solvent-oil mixture (establishedby comparison of actual plant data with the corresponding ternary diagrams for several solvent-oil combinations), it was found that the continuous countercurrent extraction of the 10- grade distillate. with N-methyl-2-pyrrolidone containing 5% water by weight, and thus having a critical solution temperatureof 240 F., gives a 77 vol. percent yield of waxy raffinate oil of 9 0 viscosity index-at 200 volume percent treat in six ideal extraction stages. Aqueous N- methyl-Z-pyrolidone containing 10% water by weight, having a critical solution temperature of 290 F., gives an 84 volume percentyield of waxy raflinate oil of 90 viscosity index at 300 volume percent treat in four ideal extraction stages.

These results may be compared with those obtained utilizing phenol to extract the same distillate at 140 F. in approximately the same number of ideal stages. In this case, a yield of only 68 volume percent viscosity index waxy product is obtained with a treat of 115 volume percent.

Example 2 To further illustrate the improved yield obtained with '6 only 54 volume percent of 90 viscosity index waxy product is obtained with a treat of 145 volume percent.

Example 3 To further illustrate the advantage of using N-methyl- 2-pyrrolidone in combination with water, a dewaxed 30- grade Western Canadian lube distillate was extracted in a crosscurrent fashion at 180 F. with aqueous N-methyl- 2-pyrrolidone containing 5% water by weight. It was found that approximately 6 crosscurrent treats of 100 volume percent each, based on the feed, were required to improve the viscosity index to 90 with a volume percent yield of 66. -By use of an established correlation between countercurrent and crosscurrent extractions the required countercurrent treat is 320 volume percent with a yield of 73 volume percent. If water is injected near the bottom of the extractor instead of premixed with N-methyl-2- pyrrolidone', the countercurrent treat is reduced to 180 volume percent with the same yield of 73 volume percent.

These results are favorable as compared with those obtained with anhydrous phenol or phenol in combination with water. Anhydrous phenol at 160 F. requires approximately three crosscurrent treats of 100 volume percent each, based on the feed, with a yield of 46 volume percent, which corresponds to 145 volume percent treat and 54% yield in countercurrent extraction. Phenol in combination with 5% water 'by weight at 180 F. requires approximately five crosscurrent treats of 100 volume percent eachwith a yield of 56 volume percent. These corres-pond to 250 volume percent treat and 64 volume per cent yield when water is premixed in countercurrent extract-ion. If water is injected near the bottom of the extractor,"the countercurrent treat is reduced to 150 volume percent with the same yield of 64 volume percent.

Example 4 The previous examples have illustrated the efliciency of NMP'and NMP/water as solvents relative to phenol and phenol/water for solvent extraction of lube oils. Several experiments were carried out in a pilot plant continuous extractor with a 600N distillate from light Arabian crude. It was found, unexpectedly, that a much higher yield of desired product was obtained, for a given amount of water in NMP, by injection of water below the NMP introduction point than by premixing the water with the NMP. Unexpectedly, the solvent treat was also much reduced. The data are tabulated in Table IV.

TABLE IV the solvent of this invention, the extraction of a 30-grade Li ht Arabian BOON distillate r {fin t 93 VI t Western Canadian lube distillate with aqueous N-methyL g curreant g f g mums 2-pyrrolidone containing 5% water by welght was m- Premixed W M t d t vestigated at an extraction temperature of 180 F. in the t e wa er same experimental manner as in Example 1. The data for Oil Solvent on Solvent Wate content 1' i ld, t, LV i 1d, the ternary diagram are summarized in Table III. NMpraotan 0 H on 3% g 5 2,59,;

58 104 58 104 TABLE In 63 143 63.5 120 Raflinate phase Extract phase 5 1 8 5 "H6 Dewaxed 66 240 eviscosity Rt u i d ingeo f Solvgertt iRgiractfivici solzlert eraoveuex o 5 w. nexoo w. ofoi18t140o F. Rpm) percent) F percent) The data are shown graphlcally 1n the figure where it 3 6 3 1 5008 98 5 may be clearly seen that water in ectlon has definite yield 53; 9 115604 9 and treat advantages over premixed water using NMP. 67. 8 9. 0 1. 5756 90. 2 56.1 11.3 1.5928 87.2 Example 5 Thus, the countercurrent extraction of the 30-grade distillates with aqueous N-methyl-Z-pyrrolidone containing 5% water by weight, having a critical solution temperature of 270 F., gives a 77 volume percent yield of waxy raffinate oil of 90 viscosity index at 200 volume percent treat in tour ideal extraction stages. These results may be compared with those obtained utilizing phenol to extract the same distillate at 180 F. in approximately the same number of ideal stages. In this case, a yield of Using the countercurrent extractor and the same lube feed oil as in Example 4, data were obtained comparing phenol/water and NMP/Water under conditions of (a) premixing the solvent and water and (b) injecting the water below the introduction point of the solvent. The data are tabulated in Table V. From the tabulated data, it is clear that (a) under equivalent conditions, NMP/ water mixtures are clearly superior extraction solvents to phenol/water mixtures, (b) water injection does not appreciably enhance the efiiciency of phenol/water systems,

7 and '(c) water'injection greatly enhances the eflici'ency of the NMP/water system. v-

TABLEV [Light Arabian 600N dlstil1ate rafiinate oil 93 VI continuouscounter current extraction] 1 What is claimed is: I

1. A countercurrent extraction process for the upgrading of a hydrocarbon oil comprising contacting said oil with a solvent comprising Nemethyl-2-pyrrolidone and Water, in an extraction zone, thereby forming a solventoilmixture, said water and said N-methyl-2-pyrrolidone introduced separately into said extraction zone and wherein said water is introduced at a point below the point of introduction of said N-methyl-Z-pyrrolidone, so as to prevent substantial mixing of said water and said N-methyl-Z-pyfrolidone prior tosaid N-methyl-2-pyrrolidone contacting said oil.

2. The process of claim 1 wherein the extraction temperature ranges between about 100 and 2570" F. v 3. The process of claim 1 wherein the amount of water present in the solvent ranges between about 0.5 wt. per cent and 30 wt. percent based on total solvent. 7

4. The process of claim 1 wherein the solvent mixture has a critical temperature of at least 200 F.

5. The process of claim 1 wherein said solvent and said oil are contacted at a treat (solvent/oil ratio) of between about 50% and 1000%.

6. The process of claim 1 wherein less than about 05% (LV) water, based on total N-methyl-Z-pyrrolidone introduced into the extraction zone, mixes with said N- *8 methyLZ-pyrrolidone,priorto said N-methyl-Z-pyrrolidone at c gthe il. I 1

7. A continuous countercurrent extraction process for the upgrading of an aromatics-containing hydrocarbon. oil selected from the group. consisting of petroleum distillate fractions and lube residua', said process comprising contacting said oil with N-methyl-Z-pyrrolidone and between about 0.5 wt. p e rcent and about 30 wt. percent water based on total solvent, inian extraction zone, thereby forming an extract phase and "a ralfinate phase, said waterand said N-methyl-Z-pyrrolidone introduced separately into said-extraction zone and wherein said 'water is introduced at a point below-the point. of introduction of said N-methyl-2- py d n s itha ssj ha about .0-5%...t .V)'-1wat r, based on total N methyl 2 pyrrolidone introduced into said 'extraction zo'ne, mixes'with said N -methyl' 2 pyrrolidone, prior to said N-methyl-2-pyrrolidone contact ing said oil, separating saidextract "and raflinate phases and recovering'an improvedhydrocarbon-oilof low aromatics content fromsa'id raffinate phase.

8. The process of claim 7 wherein the extraction tern perature ranges between about'JlOO" andZS GfF,

v I Reterences Cited i n l UNITED STATES PAIENTS 2,933,448 4/1960 Morin et a1. 208-324 2,246,297 *6/ 1941 Duncan et al L 208-324 3,262,875 7/1966 Girotti eta]. 208324 2,943,122 6/1960 Templeman et al. 208-426 3,472,757 10/1969 Morris et'al. 208-326 DELBERT E. Primary Examiner v c e. SPRESSER, 1a., Assistant Examiner I Y I U.s. c1. x11; 208 324; 260-7-674'SE 

1. A COUNTERCURRENT EXTRACTION PROCESS FOR THE UPGRADING OF A HYDROCARBON OIL COMPRISING CONTACTING SAID OIL WITH A SOLVENT COMPRISING N-METHYL-2-PYRROLIDONE AND WATER, IN AN EXTRACTION ZONE, THEREBY FORMING A SOLVENTOIL MIXTURE, SAID WATER AND SAID N-METHYL-2-PYRROLIDONE INTRODUCED SEPARATELY INTO SAID EXTRACTION ZONE AND WHEREIN SAID WATER IS INTRODUCED AT A POINT BELOW THE POINT OF INTRODUCTION OF SAID N-METHYL-2-PYRROLIDONE, SO AS TO PREVENT SUBSTANTIAL MIXING OF SAID WATER AND SAID AS TO PREVENT SUBSTANTIAL MIXNG OF SAID WATER AND SAID DONE CONTACTING SAID OIL. 